Enwei Zhu

Facile synthesis of bacterial cellulose fibres covalently intercalated with graphene oxide by one-step cross-linking for robust supercapacitors

Electrode materials with a three-dimensional network structure and high conductivity are crucial for the development of robust high-performance supercapacitors. We report the development of a facile method for the covalent intercalation of graphene oxide (GO) with bacterial cellulose (BC) fibres via a one-step esterification to construct a three-dimensional cross-linked structural scaffold. The as-prepared composite had a tensile strength of 18.48 MPa and an elongation at breakage of 24%. With an outstanding electrical conductivity of 171 S m−1, the composite electrode demonstrates a good mass-specific capacitance of 160 F g−1 at a current density of 0.4 A g−1. A robust supercapacitor was demonstrated with an outstanding capacitance retention of 90.3% over 2000 recycles. The impressive mechanical and electrochemical properties of this covalently intercalated BC/GO composite may open new avenues in developing cross-linked GO nanocomposites for stretchable electronics.

Naphthodifuran alternating quinoxaline copolymers with a bandgap of ∼1.2 eV and their photovoltaic characterization

Four new alternating copolymers of naphthodifuran and quinoxaline have been developed. With the bandgap as low as 1.2 eV, polymers exhibited extended absorption to 1200 nm. Their potential in bulk heterojunction solar cells was evaluated. With device optimization, triazoloquinoxaline based polymers contributed the highest power conversion efficiency of 0.84%.

Design and synthesis of triazoloquinoxaline polymers with positioning alkyl or alkoxyl chains for organic photovoltaics cells

Four benzodithiophene-triazoloquinoxaline alternating polymers, PBDTT-BTzQx-EH-C1, PBDT-BTzQx-EH-C1, PBDT-BTzQx-EH-C12 and PBDT-BTzQx-C12, have been designed and synthesized to investigate the correlation of alkyl side chains with the opto-electronic properties of the resulting polymers. The introduction of side chains onto the thiophene spacer or quinoxaline unit lowers the highest occupied molecular orbital energy level of the polymers, while excessive chains prevent the polymer backbone from π–π stacking and result in a decreased short circuit current and fill factor in a photovoltaic application. The bulk heterojunction cells fabricated by blending PBDTT-BTzQx-EH-C1 with [6,6]-phenyl-C61-butyric acid methyl ester exhibit a best power conversion efficiency (PCE) of 1.40%, with a short-circuit current density of 4.12 mA cm−2, an open-circuit voltage of 0.62 V and a fill factor of 55%. The device was further optimized to 2.24% PCE by using PFN (5 nm)/Ca (5 nm) as a co-interfacial layer.

Direct access to 4,8-functionalized benzo[1,2-b:4,5-b′]dithiophenes with deep low-lying HOMO levels and high mobilities

A general methodology has been proposed for the straightforward access to 4,8-functionalized benzo[1,2-b:4,5-b′]dithiophenes (BDTs) via Pd mediated coupling reactions including Suzuki–Sonogashira coupling and carbon–sulfur bond formation reactions. This versatile platform can be used to construct a library of BDT core centred conjugated systems, featuring large fused-ring structure and good charge mobility, where a hole mobility of 0.061 cm2 V−1 s−1 is demonstrated. With the energy level fine-tuned with functionalization, the charge transporting BDTs show great potential for donor–acceptor polymers.

Monosubstituted dually cationic cyclodextrins for stronger chiral recognition

Novel monosubstituted dually cationic cyclodextrins (CDs) have been synthesized by anchoring different alkyl chain spaced imidazolium and ammonium sidearm onto the CD primary ring. These cationic CDs exhibit satisfactory enantioselectivities for amino acids and acidic racemates in aqueous capillary electrophoresis.

Side-chain manipulation on accepting units of two-dimensional benzo[1,2-b:4,5-b′]dithiophene polymers for organic photovoltaics

Two donor–acceptor alternating polymers of bis(octylthio)thienyl benzo[1,2-b:4,5-b′]dithiophene (BDTTs) and fluorinated benzo[c][1,2,5]thiadiazole (fBT) or 5-dodecylthienyl-6-fluorobenzo[c][1,2,5]thiadiazole were designed for organic photovoltaic applications. The polymers displayed strong absorptions in the range of 300–650 nm and bandgaps of ∼1.60 eV. Bulk-heterojunction solar cells of PBDTTs-fBT and (6,6)-phenyl C71-butyric acid methyl ester (PC71BM) blends exhibited a maximum power conversion efficiency of 6.27%. Experimental results and theoretical modelling were correlated to reveal the impact of substitution on fluorinated BT on the optoelectronic properties of the resulting polymers.

Correlation of structure and photovoltaic performance of benzo[1,2-b:4,5-b′]dithiophene copolymers alternating with different acceptors

Four π-conjugated benzo[1,2-b:4,5-b′]dithiophene (BDT) based polymers were synthesized for application in polymer solar cells. These polymers possessed desirable HOMO/LUMO levels for polymer photovoltaic applications. PBDTT–TTz and PBDTT–DTBT displayed strong absorption in the range of 300–650 nm, while PBDTT–DPP and PBDTT–TTDPP showed a further 100 nm extended absorption band. The lowest unoccupied molecular orbital energy levels of polymers were tuned effectively from −3.34 eV to −3.81 eV by fusing with different accepting units. A maximum power conversion efficiency of 2.60% was obtained from photovoltaic cells with a PBDTT–TTz : PC61BM (1 : 2, w/w) blend film as the active layer, with a short circuit current density of 8.37 mA cm−2, an open circuit voltage of 0.70 V, and a fill factor of 44.3%.

A versatile strategy to directly synthesize 4,8-functionalized benzo[1,2-b:4,5-b′]difurans for organic electronics

A direct synthesis of 4,8-functionalized benzo[1,2-b:4,5-b′]difurans (BDFs) is developed. By fine-tuning the energy levels with different 4,8-functionalities or incorporating with electron-accepting units, BDFs show great potential as organic electronic materials, as demonstrated by 4.61% power conversion efficiency for polymer solar cells.

Triisopropylsilylethynyl substituted benzodithiophene copolymers: synthesis, properties and photovoltaic characterization

We demonstrated herein the facile synthesis of triisopropylsilylethynyl (TIPS) functionalized benzo[1,2-b:4,5-b′]dithiophene (BDT). Three new TIPSBDT-based donor–acceptor alternating copolymers were further developed by Pd-catalyzed Stille coupling. The effect of accepting unit structure on the optical, electrochemical and energy levels of the polymer was studied. The positive impact of PFN layer, high-boiling solvents processing, polar solvent treatment and solvent annealing on the performance of polymer : PC71BM bulk heterojunction solar cells was revealed. The best devices delivered a power conversion efficiency of 5.46% when blend films processed using o-dichlorobenzene with 3 vol% DIO and treated with the optimization of THF annealing and insertion of PFN layer. The device performance was correlated with the morphology evolution of blend films processed with solvent choice, methanol treatment and THF annealing.

Benzotrithiophene polymers with tuneable bandgap for photovoltaic applications

Four benzotrithiophene (BTT) based donor–acceptor polymers have been prepared by alternating with diketopyrrolopyrrole (DPP), thiazolo[5,4-d]thiazole (TTz), thieno[3,4-c]pyrrole-4,6-dione (TPD) and thiadiazolo[3,4-g]quinoxaline (DTBTQx). The BTT-based polymers possess good solubility in common organic solvents and excellent thermal stability. PBTTDPP and PBTTDTBTQx possessed an optical bandgap of 1.27 eV and 1.20 eV, with absorption spectra extending to the near-infrared region. The bulk-heterojunction solar cells delivered a highest PCE of 1.39%, with a short circuit current of 5.46 mA cm−2, an open-circuit voltage of 0.51 V and a fill factor of 0.50.